1. Field of the Invention
This invention relates to a zoom lens system, and more particularly to a short distance zoom lens having a wide angle of view and for forming an image at a predetermined short distance of an object lying at any short distance, or for forming an image at any short distance of an object lying at a predetermined short distance. Specifically, the invention relates to an enlarging lens used for enlarged printing of photographs.
2. Description of the Prior Art
As a zoom lens covering a wide angle, a lens comprising two groups, i.e. a forward group which is a divergent lens group and a rearward group which is a convergent lens group is already known and this type of zoom lens has been undergoing remarkable development. However, when such a zoom optical system is used for short distance, the forward group is moved for a magnification change. Therefore, with focusing being effected by the movement of the forward group as commonly adopted in such zoom lens systems, it is impossible to maintain the image plane always strictly at a predetermined position while zooming is being effected with respect to the object plane lying at any short distance. Moreover, if zooming is effected with respect to an object lying at a short distance, distortion varies so significantly that such conventional zoom lens systems have been unsuitable as an enlarging lens.